Incremental learning of environment interactive structures from trajectories of individuals

F ORCE FIELD TERMINOLOGY Taking into consideration a classical mechanics approach, a force is defined as a vectorial quantity that acts on a body to cause a change in its state of motion [25]. Forces can be classified in action-reaction (when bodies, which are in contact, change their momenta [25]) and action-at-a-distance forces (when objects interact without being physically touched). Considering that social interactions can be often modeled as contact-less, it becomes possible to explain social phenomena in a certain environment by modeling interactions between entities with action-at-a-distance forces. A force field null F is defined as a vector point-function which has the property that at every point of the space takes a particular value related to the magnitude and direction of a force acting on a particle of unit of mass placed there [26]. Accordingly, in this work, the particles of unit of mass affected by force fields will be called agents. A central force field null F f ( r)ˆr is a special case of force field in which the motion of agents is affected depending on the distance r to a center of force, which is generally associated with the center of mass of the object that produces the force field.